Pressure sensitive adhesives are materials which have tack properties at room temperature. The pressure sensitive adhesive firmly adheres to a variety of dissimilar surfaces without the need of more than finger or hand pressure. It is known that the adhesive should be formed of a composition with sufficient internal strength to prevent leaving a residue of the adhesive on the application surface after the adhesive has been removed. The problem of providing excellent skin adhesion with block copolymer adhesives has persisted. In addition soft polyolefin films or films produced from styrenic block copolymers cannot be used with adhesive systems which have low molecular weight components such as oil and tackifying resins unless a barrier coating is used to block migration of these components.
It is known that block copolymers of vinyl aromatic hydrocarbons and conjugated dienes make good adhesives for a number of adhesive applications. For example, styreneisoprene-styrene (SIS) triblock copolymers are known to make good adhesives for a number of tape applications such as packaging tape. However, only certain SIS adhesives systems along with a tackifing resin work well for skin adhesion and bandage applications. Prior work, such as described in U.S. Pat. No. 5,274,036, has shown that combinations of low coupling efficiency SIS polymers such as KRATON.RTM. 1112 and KRATON.RTM. 1117 block copolymers made by Shell Oil Company, with low molecular weight liquid rubbers, such as Kuraray LIR 310 (a liquid isoprene-styrene diblock copolymer), Kuraray LIR 50 (a liquid isoprene polymer), and Kuraray LIR 290 (a liquid hydrogenated isoprene polymer), have utility as medical skin adhesives because there are little or no low molecular weight species such as oil or tackifying resin which can cause skin irritation.
However, these combinations exhibit only a marginal peel strength to skin. The peel strength needs to be increased to make commercially successful products. The present invention provides a specific narrowly defined combination of low coupled SIS block copolymers with higher styrene contents than the above triblock copolymers and low molecular weight SI diblock copolymers with a low styrene content.